The waterline length (originally Load Waterline Length, abbreviated to LWL) is the length of a ship or boat at the point where it sits in the water. It excludes the total length of the boat, such as features that are out of the water. Most boats rise outwards at the bow and stern, so a boat may be quite a bit longer than its waterline length. In a ship with such raked stems, naturally the waterline length changes as the draft of the ship changes, therefore it is measured from a defined loaded condition.

Length at the waterline is often abbreviated as lwl, w/l, w.l. or wl.

This measure is essential in determining a lot of properties of a vessel, such as how much water it displaces, where the bow and stern waves are, hull speed, amount of bottom-paint needed, etc.

In sailing boats, longer waterline length will usually enable a greater maximum speed, because it allows greater sail area, without increasing beam or draft. Higher beam and draft causes higher resistance against the water. This maximum speed, also known as theoretical hull speed, can be calculated using the formula (sqrt of LWL) x 1.34.

1.
Waterline
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The waterline is the line where the hull of a ship meets the surface of the water. Temperature affects the level, because warm water provides less buoyancy, being less dense than water, as does salinity. For vessels with displacement hulls, the speed is determined by, among other things. In a sailing boat, the length can change significantly as the boat heels. The waterline can also refer to any line on a hull that is parallel to the waters surface when the ship is afloat in a normal position. Hence, all waterlines are one class of ships used to denote the shape of a hull in naval architecture plans. In aircraft design, the term refers to the vertical location of items on the aircraft. This is the Z axis of an XYZ coordinate system, the two axes being the fuselage station and buttock line. The purpose of a line is to ensure that a ship has sufficient freeboard. All commercial ships, other than in exceptional circumstances, have a load line symbol painted amidships on each side of the ship and this symbol is also permanently marked, so that if the paint wears off it remains visible. The load line makes it easy for anyone to determine if a ship has been overloaded, the exact location of the load line is calculated and verified by a classification society and that society issues the relevant certificates. This marking was invented in 1876 by Samuel Plimsoll, roman sea regulations also contained similar regulations. In the Middle Ages the Venetian Republic, the city of Genoa, in the case of Venice this was a cross marked on the side of the ship, and of Genoa three horizontal lines. The first 19th century loading recommendations were introduced by Lloyds Register of British and Foreign Shipping in 1835, Lloyds recommended freeboards as a function of the depth of the hold. These recommendations, used extensively until 1880, became known as Lloyds Rule, in the 1860s, after increased loss of ships due to overloading, a British MP, Samuel Plimsoll, took up the load line cause. In 1906, laws were passed requiring foreign ships visiting British ports to be marked with a load line and it was not until 1930 that there was international agreement for universal application of load line regulations. In 1966 the International Convention on Load Lines was concluded in London which re-examined and amended the 1930 rules, the 1966 convention has since seen amendments in 1971,1975,1979,1983,1995 and 2003, none of which have entered into force. The original Plimsoll mark was a circle with a line through it to show the maximum draft of a ship

2.
Stern
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The stern is the back or aft-most part of a ship or boat, technically defined as the area built up over the sternpost, extending upwards from the counter rail to the taffrail. The stern lies opposite of the bow, the foremost part of a ship, originally, the term only referred to the aft port section of the ship, but eventually came to refer to the entire back of a vessel. The stern end of a ship is indicated with a navigation light at night. Sterns on European and American wooden sailing ships began with two forms, the square or transom stern and the elliptical, fantail, or merchant stern. This frame is designed to support the beams that make up the stern. In 1817 the British naval architect Sir Robert Seppings first introduced the concept of the round or circular stern, the square stern had been an easy target for enemy cannon, and could not support the weight of heavy stern chase guns. The United States began building the first elliptical stern warship in 1820, USS Brandywine became the first sailing ship to sport such a stern. In naval architecture, the term transom has two meanings, in this sense, a transom stern is the product of the use of a series of transoms, and hence the two terms have blended. But until a new form of stern appeared in the 19th century, the stern was a floating house—and required just as many timbers, walls, windows. The stern frame provided the structure of the transom stern, and was composed of the sternpost, wing transom. If the stern had transoms above the transom, they would no longer be affixed to the sternpost. The first of these might be called a counter transom, next up was the window sill transom, above that, the larger the vessel, the more numerous and wider the transoms required to support its stern. Stern timbers – These timbers are mounted vertically in a series, each timber typically rests or steps on the transom and then stretches out. Those not reaching all the way to the taffrail are called short stern timbers, the two outermost of these timbers, located at the corners of the stern, are called the side-counter timbers or outer stern timbers. The flat surface of any transom stern may begin either at or above the waterline of the vessel. The geometric line which stretches from the transom to the archboard is called the counter. The visual unpopularity of Seppings circular stern was soon rectified by Sir William Symonds, in this revised stern, a set of straight post timbers stretches from the keel diagonally aft and upward. It rests on the top of the sternpost and runs on either side of the rudder post to a point well above the vessels waterline, the finished stern has a continuous curved edge around the outside and is raked aft

3.
Twenty-foot equivalent unit
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The twenty-foot equivalent unit is an inexact unit of cargo capacity often used to describe the capacity of container ships and container terminals. Also, it is common to designate 45-foot containers as 2 TEU, the standard intermodal container is designated as twenty feet long and 8 feet wide. The twistlocks on a ship are put at a distance so that two standard twenty-foot containers have a gap of three inches which allows a single forty-foot container to be put on top, the forty-foot containers have found wider acceptance, as they can be pulled by semi-trailer truck. The length of such a combination is within the limits of national road regulations in many countries, requiring no special permission. As some road regulations allow longer trucks, there are variations of the standard forty-foot container — in Europe. Containers with a length of 48 feet or 53 feet are restricted to transport in the United States. Although longer than 40 feet, these variants are put in the class of forty-foot equivalent units. Container ships only take 40-foot and 20-foot containers below deck, plus 45-foot containers above deck, ninety percent of the containers that container ships carry are 40-foot units. As container ships carry 90% of the freight, at least 81% of the worlds freight moves via 40-foot containers. As the TEU is a unit, it cannot be converted precisely into other units. The related unit forty-foot equivalent unit, however, is defined as two TEU, the most common dimensions for a 20-foot container are 20 feet long,8 feet wide, and 8 feet 6 inches high, for a volume of 1,360 cubic feet. However, both 9-foot-6-inch-tall High cube and 4-foot-3-inch half height containers are also reckoned as 1 TEU and this gives a volume range of 680 to 1,520 cubic feet for one TEU. While the TEU is not itself a measure of mass, some conclusions can be drawn about the mass that a TEU can represent. The maximum gross mass for a 20-foot dry cargo container is 24,000 kilograms, subtracting the tare mass of the container itself, the maximum amount of cargo per TEU is reduced to approximately 21,600 kilograms. Similarly, the gross mass for a 40-foot dry cargo container is 30,480 kilograms. After correcting for tare weight, this gives a capacity of 26,500 kilograms. Twenty-foot, heavy tested containers are available for goods such as heavy machinery. These containers allow a maximum weight of 67,200 pounds, an empty weight of 5,290 pounds, Container ship Container terminal Containerization List of unusual units of measurement Panama Canal toll system shipping ton Maersk Shipping

4.
Intermodal container
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These containers are known under a number of names, such as simply container, cargo or freight container, ISO container, shipping, sea or ocean container, container van or box, sea or c can. The common heights are 8 feet 6 inches and 9 feet 6 inches – the latter are known as High Cube or Hi-Cube containers, in 2012 there were about 20.5 million intermodal containers in the world of varying types to suit different cargoes. Containers have largely supplanted the traditional break bulk cargo – in 2010 containers accounted for 60% of the seaborne trade. The predominant alternative methods of transport carry bulk cargo – whether gaseous, liquid or solid – e. g. by bulk carrier or tank ship, for air freight, the more light-weight IATA-defined unit load device is used. By the 1830s, railways on several continents were carrying containers that could be transferred to other modes of transport, the Liverpool and Manchester Railway in the United Kingdom was one of these. Simple rectangular timber boxes, four to a truck, they were used to convey coal from the Lancashire collieries to Liverpool, early versions of standardized containers were used in Europe before World War II. Construction of these containers had a frame with wooden walls, floor, roof. American containers at this time were not standardized, and these early containers were not yet stackable – neither in the U. S. nor Europe, in November 1932, the first container terminal in the world was opened by the Pennsylvania Rail Road Company in Enola, PA. A system was selected for Western Europe, based on the Netherlands system for goods and waste transportation called Laadkisten. This system used roller containers for transport by rail, truck and ship, in various configurations up to 5,500 kg capacity and this became the first post World War II European railway standard of the International Union of Railways – UIC-590, known as pa-Behälter. It was implemented in the Netherlands, Belgium, Luxembourg, West Germany, Switzerland, Sweden, the use of standardized steel shipping containers began during the late 1940s and early 1950s, when commercial shipping operators and the US military started developing such units. In 1948 the U. S. Army Transportation Corps developed the Transporter, a rigid, corrugated steel container, able to carry 9,000 pounds. It was 8 ft 6 in long,6 ft 3 in wide, and 6 ft 10 in high, with doors on one end, was mounted on skids. After proving successful in Korea, the Transporter was developed into the Container Express box system in late 1952, cONEXes could be stacked three high, and protected their contents from the elements. By 1965 the US military used some 100,000 Conex boxes, making this the first worldwide application of intermodal containers. From 1949 onwards, engineer Keith Tantlinger repeatedly contributed to the development of containers, as well as their handling, steel castings on the top corners provided lifting and securing points. In 1955 trucking magnate Malcom McLean bought Pan-Atlantic Steamship Company, to form a container shipping enterprise, the first containers were supplied by Brown, where McLean met Keith Tantlinger, and hired him as vice-president of engineering and research. Under the supervision of Tantlinger, a new 35 ft x 8 ft x 8 ft 6 in Sea-Land container was developed, each container had a frame with eight corner castings that could withstand stacking loads

5.
Displacement (ship)
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The displacement or displacement tonnage of a ship is the ships weight. The name reflects the fact that it is measured indirectly, by first calculating the volume of water displaced by the ship, by Archimedes principle, this is also the weight of the ship. Displacement should not be confused with other measurements of volume or capacity typically used for vessels such as net tonnage, gross tonnage. The process of determining a vessels displacement begins with measuring its draft This is accomplished by means of its draft marks, a merchant vessel has three matching sets, one mark each on the port and starboard sides forward, midships, and astern. These marks allow a ships displacement to be determined to an accuracy of 0. 5%, the draft observed at each set of marks is averaged to find a mean draft. The ships hydrostatic tables show the corresponding volume displaced, to calculate the weight of the displaced water, it is necessary to know its density. Seawater is more dense than water, so a ship will ride higher in salt water than in fresh. The density of water varies with temperature. Devices akin to slide rules have been available since the 1950s to aid in these calculations and it is done today with computers. Displacement is usually measured in units of tonnes or long tons and these bring the ship down to its load draft, colloquially known as the waterline. Full load displacement and loaded displacement have almost identical definitions, full load is defined as the displacement of a vessel when floating at its greatest allowable draft as established by classification societies. Warships have arbitrary full load condition established, deep load condition means full ammunition and stores, with most available fuel capacity used. Light displacement is defined as the weight of the ship excluding cargo, fuel, water, ballast, stores, passengers, crew, normal displacement is the ships displacement with all outfit, and two-thirds supply of stores, ammunition, etc. on board. Standard displacement, also known as Washington displacement, is a term defined by the Washington Naval Treaty of 1922. Naval architecture Hull Hydrodynamics Tonnage Dear, I. C. B, oxford Companion to Ships and the Sea. George, William E. Stability & Trim for the Ships Officer, turpin, Edward A. McEwen, William A. Trim and Stability Information for Drydocking Calculations, conference on the Limitation of Armament,1922. Papers Relating to the Foreign Relations of the United States,1922, proceedings of the United States Naval Institute

6.
Panamax
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Panamax and New Panamax are terms for the size limits for ships travelling through the Panama Canal. Formally, these limits and requirements are published by the Panama Canal Authority and these requirements also describe topics like exceptional dry seasonal limits, propulsion, communications, and detailed ship design. These dimensions give clear parameters for ships destined to traverse the Panama Canal and have influenced the design of ships, naval vessels. Panamax specifications have been in effect since the opening of the canal in 1914, in 2009 the ACP published the New Panamax specification which came into effect when the canals third set of locks, larger than the original two, opened on 26 June 2016. Ships that do not fall within the Panamax-sizes are called post-Panamax, because the largest ships traveling in opposite directions cannot pass safely within the Culebra Cut, the canal effectively operates an alternating one-way system for these ships. Panamax is determined principally by the dimensions of the original lock chambers, each of which is 110 ft wide,1,050 ft long. The usable length of each chamber is 1,000 ft. The available water depth in the lock chambers varies, but the shallowest depth is at the sill of the Pedro Miguel Locks and is 41.2 ft at a Miraflores Lake level of 54 ft 6 in. The clearance under the Bridge of the Americas at Balboa is the factor on a vessels overall height for both Panamax and Neopanamax ships, the exact figure depends on the water level. New Panamax increases allowable width to 49 m.39.5 ft in Tropical Fresh Water, the name and definition of TFW is created by ACP using the freshwater Lake Gatún as a reference, since this is the determination of the maximum draft. The salinity and temperature of water affect its density, and hence how deep a ship will float in the water, Tropical Fresh Water is fresh water of Lake Gatún, with density 0.9954 g/cm3, at 29.1 °C. The physical limit is set by the entrance of the Pedro Miguel locks. When the water level in Lake Gatún is low during a dry season the maximum permitted draft may be reduced. Such a restriction is published three weeks in advance, so ship loading plans can take appropriate measures, New Panamax increases allowable draft to 15. 190 ft measured from the waterline to the vessels highest point, limit also pertains to New Panamax, exception,205 ft when passage at low water at Balboa is possible. All exceptions are allowed only after specific request and an investigation. A Panamax cargo ship would typically have a DWT of 65, 000–80,000 tonnes, New Panamax ships can carry 120,000 DWT. Panamax container ships can carry 5,000 twenty-foot equivalent units, the longest ship ever to transit the original locks was San Juan Prospector, now Marcona Prospector, an ore-bulk-oil carrier that is 973 ft long, with a beam of 106 ft

7.
Oil tanker
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An oil tanker, also known as a petroleum tanker, is a merchant ship designed for the bulk transport of oil. There are two types of oil tankers, crude tankers and product tankers. Crude tankers move large quantities of unrefined oil from its point of extraction to refineries. Product tankers, generally smaller, are designed to move refined products from refineries to points near consuming markets. Oil tankers are often classified by their size as well as their occupation, the size classes range from inland or coastal tankers of a few thousand metric tons of deadweight to the mammoth ultra large crude carriers of 550,000 DWT. Tankers move approximately 2,000,000,000 metric tons of oil every year, second only to pipelines in terms of efficiency, the average cost of oil transport by tanker amounts to only two or three United States cents per 1 US gallon. Some specialized types of oil tankers have evolved, one of these is the naval replenishment oiler, a tanker which can fuel a moving vessel. Combination ore-bulk-oil carriers and permanently moored floating storage units are two variations on the standard oil tanker design. Oil tankers have been involved in a number of damaging and high-profile oil spills, as a result, they are subject to stringent design and operational regulations. The technology of oil transportation has evolved alongside the oil industry, although anthropogenic use of oil reaches to prehistory, the first modern commercial exploitation dates back to James Youngs manufacture of paraffin in 1850. In the early 1850s, oil began to be exported from Upper Burma, the oil was moved in earthenware vessels to the river bank where it was then poured into boat holds for transportation to Britain. In the 1860s, Pennsylvania oil fields became a supplier of oil. Break-bulk boats and barges were used to transport Pennsylvania oil in 40-US-gallon wooden barrels. But transport by barrel had several problems, the first problem was weight, the standard empty barrel weighed 64 pounds, representing 20% of the total weight of a full barrel. Other problems with barrels were their expense, their tendency to leak, the expense was significant, for example, in the early years of the Russian oil industry, barrels accounted for half the cost of petroleum production. In 1863, two tankers were built on Englands River Tyne. These were followed in 1873 by the first oil-tank steamer, Vaderland, the vessels use was curtailed by U. S. and Belgian authorities citing safety concerns. By 1871, the Pennsylvania oil fields were making limited use of oil tank barges, the modern oil tanker was developed in the period from 1877 to 1885

8.
Hull (watercraft)
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The hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present, the line where the hull meets the water surface is called the waterline. The structure of the hull varies depending on the vessel type, the uppermost continuous deck may be called the upper deck, weather deck, spar deck, main deck, or simply deck. The particular name given depends on the type of ship or boat. In a typical wooden sailboat, the hull is constructed of wooden planking, supported by transverse frames and bulkheads, often but not always there is a centerline longitudinal member called a keel. In fiberglass or composite hulls, the structure may resemble wooden or steel vessels to some extent, in many cases, composite hulls are built by sandwiching thin fiber-reinforced skins over a lightweight but reasonably rigid core of foam, balsa wood, impregnated paper honeycomb or other material. The shape of the hull is entirely dependent upon the needs of the design, shapes range from a nearly perfect box in the case of scow barges, to a needle-sharp surface of revolution in the case of a racing multihull sailboat. Hulls come in varieties and can have composite shape, but are grouped primarily as follows. Examples are the flat-bottom, v-bottom, and multi-bottom hull and these types have at least one pronounced knuckle throughout all or most of their length. These hull shapes all have smooth curves, examples are the round bilge, semi-round bilge, and s-bottom hull. After this they can be categorized as, Displacement The hull is supported exclusively or predominantly by buoyancy, vessels that have this type of hull travel through the water at a limited rate that is defined by the waterline length. They are often, though not always, heavier than planing types, planing The planing hull form is configured to develop positive dynamic pressure so that its draft decreases with increasing speed. The dynamic lift reduces the surface and therefore also the drag. They are sometimes flat-bottomed, sometimes V-bottomed and more rarely, round-bilged, the most common form is to have at least one chine, which makes for more efficient planing and can throw spray down. Planing hulls are more efficient at speeds, although they still require more energy to achieve these speeds. An effective planing hull must be as light as possible with flat surfaces that are consistent with sea keeping. Sail boats that plane must also sail efficiently in displacement mode in light winds, semi-displacement, or semi-planing The hull form is capable of developing a moderate amount of dynamic lift, however, most of the vessels weight is still supported through buoyancy. At present, the most widely used form is the round bilge hull, in the inverted bell shape of the hull, with a smaller payload the waterline cross-section is less, hence the resistance is less and the speed is higher

9.
Panama Canal
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The Panama Canal is an artificial 48-mile waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean. The canal cuts across the Isthmus of Panama and is a key conduit for maritime trade. The original locks are 33.5 metres wide, a third, wider lane of locks was constructed between September 2007 and May 2016. The expanded canal began operation on June 26,2016. The new locks allow transit of larger, Post-Panamax ships, capable of handling more cargo, France began work on the canal in 1881 but stopped due to engineering problems and a high worker mortality rate. The United States took over the project in 1904 and opened the canal on August 15,1914, Colombia, France, and later the United States controlled the territory surrounding the canal during construction. The U. S. continued to control the canal and surrounding Panama Canal Zone until the 1977 Torrijos–Carter Treaties provided for handover to Panama. After a period of joint American–Panamanian control, in 1999 the canal was taken over by the Panamanian government and is now managed and operated by the government-owned Panama Canal Authority. Annual traffic has risen from about 1,000 ships in 1914, by 2012, more than 815,000 vessels had passed through the canal. It takes six to eight hours to pass through the Panama Canal, the American Society of Civil Engineers has called the Panama Canal one of the seven wonders of the modern world. Such a route would have given the Spanish a military advantage over the Portuguese, during an expedition from 1788 to 1793, Alessandro Malaspina outlined plans for its construction. Given the strategic location of Panama and the potential offered by its narrow isthmus separating two great oceans, other links in the area were attempted over the years. The ill-fated Darien scheme was launched by the Kingdom of Scotland in 1698 to set up a trade route. Generally inhospitable conditions thwarted the effort, and it was abandoned in April 1700, another effort was made in 1843. They referred to it as the Atlantic and Pacific Canal and it was a wholly British endeavor and it was expected to be completed in five years, but the plan was never carried out. At nearly the same time, other ideas were floated, including a canal across Mexicos Isthmus of Tehuantepec. Nothing came of that plan either. )In 1846 the Mallarino–Bidlack Treaty, negotiated between the U. S. and New Granada, granted the United States transit rights and the right to intervene militarily in the isthmus. In 1849, the discovery of gold in California created great interest in a crossing between the Atlantic and Pacific Oceans, the Panama Railway was built by the United States to cross the isthmus and opened in 1855

10.
Suezmax
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Suezmax is a naval architecture term for the largest ship measurements capable of transiting the Suez Canal in a laden condition, and is almost exclusively used in reference to tankers. Since the canal has no locks, the only serious limiting factors are draft, the current channel depth of the canal allows for a maximum of 20. The canal was deepened in 2009 from 18 to 20 metres, the typical deadweight of a Suezmax ship is about 160,000 tons and typically has a beam of 50 m. Also of note is the maximum head room—air draft—limitation of 68 m, Suez Canal Authority produces tables of width and acceptable draft, which are subject to change. The similar terms Panamax, Malaccamax, and Seawaymax are used for the largest ships capable of fitting through the Panama Canal, aframax tankers are those with a capacity of 80,000 tonnes deadweight to 120,000 DWT. The term Chinamax refers to vessels able to use a number of harbours while fully laden, Capesize refers to bulk carriers too big to pass through the Suez Canal—and needing to go around the Cape of Good Hope—but recent dredging means many Capesize vessels can use the canal. Plans to deepen the draft to 70 feet could lead to a redefinition of the Suezmax specification, list of Panamax ports Cargo ship size categories Ship sizes

The metacentric height (GM) is a measurement of the initial static stability of a floating body. It is calculated as …

Initially the second moment of area increases as the surface area increases, increasing BM, so Mφ moves to the opposite side, thus increasing the stability arm. When the deck is flooded, the stability arm rapidly decreases.

Distance GZ is the righting arm: a notional lever through which the force of buoyancy acts